Solid-state laser with spatially-tailored active ion concentration using valence conversion with surface masking and method

Abstract

A material having a surface and a dopant in the material distributed whereby the material has a spatially variant optical flux density profile. In accordance with the invention, tailored non-uniform gain profiles within a Yb:YAG laser component (rod, slab, disc, etc.) are achieved by a spatial material modification in the spatially masked pre-forms. High temperature-assisted reduction leads to the coordinate-dependent gain profiles, which are controlled by the topology of the deposited solid masks. The gain profiles are obtained by reducing the charge state of the laser-active trivalent Yb3+ ions into inactive divalent Yb2+ ions. This valence conversion process is driven by mass transport of ions and oxygen vacancies. These processes, in turn, affect the dopant distribution throughout the surface and bulk laser crystal. By reducing proportionally more Yb3+ ions at the unmasked areas of component, than in the masked areas, the coordinate-dependent or spatially-controlled gain profiles are achieved. Preferred masking materials are high temperature ceramic glazes and glasses. The masking includes the fabrication of frit, mixing this frit with de-ionized water to form slurry, deposition of the slurry on the surface of laser component or pre-form, and a heat treatment (firing) of the deposited layer. The invention can be used for the fabrication of laser rods, slabs, etc. with various concentrations and spatial localizations of dopants.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to high-energy lasers. More specifically, the present invention relates to the fabrication of solid-state laser crystal and ceramic components and pre-forms having non-uniform gain profiles. [0003] 2. Description of the Related Art [0004] High-energy lasers (HELs) are currently being evaluated for military and industrial applications. Solid-state lasers have shown considerable promise for this application. A solid-state laser typically includes a laser amplifier mounted within a laser resonator. The resonator provides the feedback necessary to build oscillation within the laser. The bulk laser active medium of the laser amplifier may be in the shape of a slab, rod or disk. When pumped, the medium provides amplification. The provision of reflective gratings at the ends of the active medium provides a resonator. [0005] In a typical laser, an incoherent light source imparts energy to the l...

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Benefits of technology

[0016] In an illustrative embodiment, the spatially variant profile is effected with a spatially dependent mask. The dopant has a first species at a first valence state and a second species at a second valence state. The concentration of said dopant species at said first valence state increases with distance from said surface and the concentration of said dopant species at said second valence state decreases with distance from said surface.

[0017] In the illustrative embodiment, coordinate-dependent gain profiles are obtained by heat treatment of spatially masked Yb:YAG crystals or Yb-doped Y(sub 3)Al(sub 5)O(sub 12) ceramics in a reducing environment. The treatment leads to conversion of the laser-active trivalent Yb3+ ions into inactive divalent Yb2+ ions due to the thermally activated mass transport of ions and oxygen vacancies in the unmasked zones. The masks may be thick coatings of high temperature glasses and oxide ceramics.

[0018] In accordance with the invention, tailored non-uniform gain profiles within a Yb:YAG laser component (rod, slab, disc, etc.) are achieved by a spatial material modification in the spati

Problems solved by technology

Thus, when such a crystal is side-pumped, non-uniform absorption and thus non-uniform gain often result, with the highest gain being near the edge of the lasing medium.

The concentration of gain near the edge of the medium leads to problems with parasitic oscillation and amplified spontaneous emission (ASE), extraction, efficiency, and beam quality (mode control).

This is particularly problematic with respect to rod shaped media.

However, problems with intra-cavity apertures have been encountered including losses, active alignment and the possibility of damage, as the result of the introduction of such components into the resonator.

Custom or specific resonator point designs for optimal performance at a specific output power are problematic inasmuch as such designs are, by definition, only suitable for one power, and therefore are especially susceptible to performance degradation as the resonator or pump cavity components change.

Unfortunately, crystal and ceramic rods having radially-dependent gain profiles in accordance with the method taught in the '462 application have created other problems due to the fact that the valence conversion effected thereby on the end faces and ends of the barrels of the rods may adversely affect the operation of the laser.

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